Barcelona has an option to make the move permanent next summer at a reported fee of €30 million. The club will also cover Rashford's wages for the duration of the loan.
Rashford has reportedly taken a 25 per cent pay cut to join the Spanish team. This is his second consecutive loan spell, following a stint at Aston Villa last season.
Rashford had been looking to leave Manchester United this summer, with his number 10 shirt handed to new signing Matheus Cunha. However, Barcelona's current financial situation means they cannot register Rashford for LaLiga competition.
LaLiga's financial rules require clubs to only spend what they earn, forcing Barcelona to find alternative revenue streams or sell players to accommodate new signings.